1. Field of the Invention
The present invention relates generally to a method for controlling power in a radio communication system, and more particularly a method for controlling power in a CDMA (Code Division Multiple Access) telecommunications system.
2. Description of the Related Art
Radio communication systems control power according to two methods, such as Forward Link Power Control and Reverse Link Power Control. Generally, in such power control the distance of a terminal from a base station is varied as the terminal moves and thus control thereon is required. Even if the terminal remains in the same position, power control between the mobile terminal and the base station is required as other mobile substances constantly change an environment of radio channels. The base station and the terminal can process received signals and reduce error rate more effectively via power control. Now, performing reverse power control in a CDMA system with reference to FIG. 1 and FIG. 2 will be described.
FIG. 1 is a block diagram illustrating reverse closed loop power control in a CDMA system according to the related art. FIG. 1 is provided only for showing a configuration for reverse closed loop power control. The reference numeral 10 designates only a section for power control in the base station in a function block. The reference numeral 20 designates only a section for power control in the terminal in a function block.
A noise-to-power ratio measuring unit 12 in the base station inspects a ratio of noise-to-power of the received signal and outputs the measured value. Such output data is outputted to a PCB determining unit 14 for determining a PCB (Power Control Bit). The PCB determining unit 14 uses the received signal to determine the PCB and outputs the determined PCB to a data transmission unit 16. The data transmission unit 16 transmits the bit for controlling power of the data via a power control sub-channel Since the signal is transmitted under a radio environment, noise and delay take place in the channel. Such delay can be expressed as noise, and addition of noise can be simplified as being processed in an adder 18. Therefore, noise is added in the adder 18 to be inputted to a PCB detecting unit 22 of the terminal.
The PCB detecting unit 22 receives the signal transmitted on the radio environment and detects the PCB from the received signal. The signal detected is input to a transmission power adjusting unit 24. The transmission power adjusting unit 24 controls power subject to transmission according to the received value. In other words, the terminal 20 power controls data subject to transmission based upon the received power control bit, and transmits data of the power controlled value to the base station. Accordingly, the base station receives and processes the signal synthesized with noise.
FIG. 2 is a flow chart illustrating a power control process in the base station according to the related art. Herein below, the power control process in the base station according to the related art will be described with reference to FIG. 1 and FIG. 2.
In step 100, the noise-to-power ratio measuring unit 12 of the terminal 10 receives the signals transmitted via the radio environment to measure the ratio of noise-to-power, which is later output to the PCB determining unit 14. Then in step 102, the PCB determining unit 14 compares the measured value with a predetermined threshold value. If the measured value is smaller than the threshold value, the process proceeds to step 104 to determine the PCB to be decreased. If the measured value is at least the threshold value, the process proceeds to step 106 to determine the PCB to be increased. Upon such determination, the data transmission unit 16 transmits the determination to the terminal via the transmission channel in the radio environment.
Such power control is carried out in one, two or three kinds of step sizes. In other words, the amount of variation in power control is carried out within the predetermined one, two or three steps. However, time delay takes place according to the distance between the radio terminal and the base station when the foregoing bit is power transmitted. This time delay, essentially, takes place in proportion to distance between the radio terminal and the base station. Also, time is required for treating the time delay between the base station and the terminal, resulting in further delay in addition to the transmission time delay. Such an error in power control is a factor that reduces radio conversation qualities.